1. Field of the Invention
The invention relates to a process for detecting and correcting a change in the fiber orientation cross-direction profile of a paper or cardboard web in the manufacturing process of a paper or cardboard machine. Furthermore, the invention relates to a device for detecting and correcting a change in the fiber orientation cross-direction profile in the manufacturing process.
2. Discussion of Background Information
In the manufacture of a paper or cardboard web, there are a large number of interfering factors in the manufacturing process, which can negatively influence the web properties of the paper or cardboard web with regard to its uniformity over the width of the machine used in the manufacture of the web. These interfering factors include, for example, temperature fluctuations, pressure fluctuations, and manufacture tolerances, but also include changes to the machine due to constant wear. Two significant web properties that influence the quality of the paper produced are the desirable, mostly uniform mass distribution of the paper and the desirable, mostly uniform orientation of the fibers in the paper.
The uniform mass distribution assures a favorable basis weight cross-direction profile and a corresponding uniform thickness of the paper layer, while a uniform and correctly aligned fiber orientation has a significant influence on the breaking length ratio, the xe2x80x9ccurlxe2x80x9d of copier papers, and also the running properties of roll papers. In this connection, reference is made to the publications by Robert A. Braun, APPITA 1995, 229 to 234; Scott B. Pantaleo, TAPPI Proceedings, 1994, 259 to 264, and Wochenblatt fxc3xcr Papierfabrikation [Weekly of Paper Manufacturing] 123, February 1995, No. 4, pp. 121 to 126.
For detecting and influencing a web properties profile, such as the basis weight cross-direction profile of a paper or cardboard web, patent document DE 35 35 849 has disclosed measuring the basis weight cross-direction profile of a paper web and, in accordance with the desired change, altering the width of the outlet gap of a headbox at particular locations on the web width so that the flow rate of the stock suspension correspondingly changes locally. The change in the flow rate of the stock suspension, with an even concentration over the width of the web manufacturing machine, influences the quantity of solids at locations on the web and consequently produces an adjustment of the basis weight cross-direction profile.
Patent document DE 40 19 593 A1 discloses a device and a process for regulating the basis weight profile of the web. In this process, when there is a variation of the basis weight profile of the paper web at a particular location on the web width, the concentration of the stock suspension flow should be changed at the particular location. In order to achieve this, a proposal has been made to section the headbox, at least partially, over the width of the machine and to charge the headbox with individually adjustable concentrations with the aid of regulated sectional flows. The individual adjustment of the concentration of the respective sectional flows is carried out by regulating the influx ratios of two individual flows with constant, but different concentrations. The differing content of the sectional flows as regards fibrous material, such as ash and other additives, produces a change in the basis weight at the corresponding location on or across the web width.
Regulating processes for sectional adjustment of headboxes have been disclosed, for example, in patent documents DE 42 38 037 and DE 40 05 281. In these regulating processes, the basis weight cross-direction profile in the paper web is respectively measured and, in accordance with the changes in the basis weight cross-direction profile from the ideal state, the corresponding actuators in the headbox are adjusted in order to achieve the desired basis weight cross-direction profile.
A similar control/regulation device as well as a process for regulating the basis weight cross-direction profile and the fiber orientation cross-direction profile has been disclosed by patent document DE 42 39 845. This document provides for embodying the headbox likewise, at least partially, in sections and influencing the paper stock suspension in its consistency and/or fiber orientation in the individual sections by a supply of dilution water or other fluids in order to regulate the corresponding cross-direction profile. This document, though, does not indicate how the change in a fiber orientation cross-direction profile can be measured.
Furthermore, reference is made to patent document DE 196 34 997, which describes a regulating device with a number of measurement sensors and a process for regulating different web property profiles. The measurement process described in this document, by a number of measurement sensors for determination of the web thickness, describes a measurement process for determining separate basis weight cross-direction profiles and basis weight longitudinal direction profiles in a paper web, wherein the basis weight cross-direction profiles determined by this procedure can be represented free of components of the basis weight longitudinal direction profile. A similar process has also been disclosed by DE 20 19 975.
Patent document DE 196 34 996, which discloses a sectional stock density-regulated headbox with a paper stock consistency regulation. Likewise, patent documents DE 42 11 291 and DE 42 11 290 disclose a sectional stock density regulation of a headbox, with a single valve per section with uniform volume flow. Patent documents DE 40 19 593 and DE 41 12 347 disclose a stock density regulation and volume flow regulation for a sectioned headbox with two valves per section.
The disclosure of the above-discussed documents is expressly incorporated by reference herein in their entirety.
The above-discussed background information does, in fact, represent a number of possibilities with which a fiber orientation cross-direction profile of a paper web can be influenced by the headbox, but none of the foregoing documents explain how a change in the fiber orientation cross-direction profile or the fiber orientation cross-direction profile itself can be measured xe2x80x9con linexe2x80x9d during the operation of the paper machine that forms the web. The currently known measuring methods of the fiber orientation cross-direction profile cannot be carried out xe2x80x9con linexe2x80x9d or else would require an extremely high degree of expense.
There is the problem, therefore, that before a proper continuous regulation of the fiber orientation cross-direction profile can be carried out in an operating paper machine, a reasonably priced process is required for detecting a change in a fiber orientation cross-direction profile.
Thus, an aspect of the invention is to provide a reasonably priced process, which can also be carried out xe2x80x9con linexe2x80x9d, for detecting a change in the fiber orientation cross-direction profile of a paper or cardboard web in the manufacturing process on a paper or cardboard manufacturing machine. Likewise, another object of the invention is to provide a process that can be carried out xe2x80x9con linexe2x80x9d for correcting a change in the fiber orientation cross-direction profile or a corresponding regulating process for a preset fiber orientation cross-direction profile. Another object of the invention is to provide devices for carrying out the process according to the invention.
The first aspect of the invention is to provide a process for detecting a change in the fiber orientation in a paper or cardboard web in the manufacturing process of a paper or cardboard web by a machine in which a change in the fiber orientation cross-direction profile in the web is inferred by way of a characteristic change in the basis weight cross-direction profile or at least one measurement quantity that correlates thereto and/or by way of a characteristic change in the basis weight in the travel direction of the web or at least one measurement quantity that correlates thereto.
The inventors of the present invention have recognized that it is possible, during the manufacture of the paper web, to infer or determine a possibly occurring change in the fiber orientation cross-direction profile by analysis of the change in the basis weight cross-direction profile and/or the analysis of the basis weight longitudinal direction profile, i.e. the chronological course of the basis weight.
If the reasons that are causally related to a change in the fiber orientation cross-direction profile of a paper web in the manufacturing process are taken into consideration, then it turns out that as a rule, they correspond to a deformation of the headbox. For the most part, a deformation of the headbox occurs in continuous operation when a temperature change and/or a pressure change occurs in the headbox and, therefore, a change in the headbox geometry occurs. On the one hand, changes of this kind have a characteristic chronological course and on the other hand, they also have a characteristic change profile, i.e. these changes occur over characteristic widths of the web or have characteristic wavelengths.
It is consequently possible to infer or determine a change in the fiber orientation or the fiber orientation cross-direction profile by measuring and evaluating the changes in the basis weight cross-direction profile and/or the changes in the basis weight longitudinal direction profile, i.e. the change in the basis weight in the chronological course of the manufacturing process.
An analysis of the basis weight cross-direction profile can, for example, be carried out by a Fourier analysis. The Fourier analysis supplies a characteristic wavelength spectrum of the changes. If these changes occur in a wavelength range that is greater than a defined critical wavelength, then a change in the fiber orientation cross-direction profile can be inferred or determined with great reliability. The critical wavelength starting from which a change in the fiber orientation cross-direction profile is inferred or determined varies individually from headbox to headbox, since in this connection the respective, structurally conditional embodiments have an influence on the type of deformation of the headbox. It is therefore necessary to precisely define this critical wavelength experimentally. In a first approximation, though, it can be assumed that the critical wavelength lies in the range from about at least 0.5 meters or about at least ⅕ the headbox width, preferably about xc2xd the inside width (machine width) of the headbox nozzle.
In this connection, it should be noted that the smaller the distance of the measurement of the basis weight cross-direction profile or a measurement quantity that correlates to the basis weight cross-direction profile from the headbox, the greater the fundamental positive effect on the decision process. If the measurement of the basis weight cross-direction profile is only carried out at the end of the paper machine, then a decision with a high degree of success probability is in fact still possible, but the uncertainty increases since other influences coming from the machine after the headbox can cause disruptions.
Correspondingly, another process is proposed for detecting a change in the fiber orientation of a paper or cardboard web in the manufacturing process, which includes at least the following process steps:
repeatedly determining the basis weight cross-direction profile of the web;
determining the change(s) in the basis weight cross-direction profile;
determining the wavelength(s) xcex of the change(s) in the basis weight cross-direction profile; and,
comparing the wavelength(s) of the change(s) in the basis weight cross-direction profile to a predetermined value raster for deciding whether the respective change corresponds to a change in the fiber orientation cross-direction profile.
According to a concept of the invention, it is furthermore also possible to infer or determine a change in the fiber orientation cross-direction profile if only the basis weight longitudinal direction profile is observed in the manufacturing process of the paper web, i.e. the chronological course of the basis weight at a particular position on or across the machine width. If the causes for the change are considered, it turns out that essentially three groups of changes are possible.
There can be instabilities in the constant part of the paper machine. As a rule, these changes occur at relatively high change speeds, preferably greater than about 0.5 g/m2 per minute. These changes are not connected to a change in the fiber orientation cross-direction profile. Also, gradual changes in the basis weight, preferably with change speeds of less than about 0.5 g/m2 per a ten (10) hour interval. These changes indicate an influence from the dewatering conditions in the wet section, for example a continuous screen wear, and do not correspond to a change in the fiber orientation cross-direction profile. Another change is in the basis weight with change speeds between the first and second range discussed. As a rule, these changes indicate a deformation of the headbox geometry, which mostly occurs due to temperature fluctuations. These kinds of changes to the headbox geometry simultaneously induce a change in the nozzle outlet gap and corresponding lateral flow components in the nozzle of the headbox, which in turn lead to a change in the fiber orientation cross-direction profile.
Due to these facts, the invention also proposes a process for detecting a change in the fiber orientation of a paper or cardboard web in the manufacturing process, which includes the following process steps: determining the chronological course of the basis weight of the web in at least one position on the machine width (basis weight longitudinal direction profile); determining the chronological change(s) in the basis weight in the at least one position; determining the change speed xcex94FG/xcex94t or the relative change speed of the basis weight in this at least one location; and, comparing the change speed(s) to a predetermined value raster for deciding whether the respective change speed can correspond to a change in the fiber orientation cross-direction profile. For example, the percentage change in the basis weight in relation to the average value of the basis weight over the entire machine width can be enlisted or used as a relative change speed. However, other fixed, predetermined basis weight values can also be used as a reference point.
It is noted that the term xe2x80x9cdeterminingxe2x80x9d is not absolutely intended to mean an exact measurement of the basis weight, but that other measurement quantities that correlate to the basis weight can also be used since in this instance, only a determination of the change in the basis weight is required and not an absolute measurement of the basis weight.
An improvement on the two processes for detecting a change in the fiber orientation cross direction profile can be achieved by a combination of these two processes. In this connection, an actual change in the fiber orientation cross-direction profile is assumed if the conditions of the criteria of both of the processes are met.
A further improvement of the detection process of a change in the fiber orientation in a paper web can be achieved by virtue of the fact that with the aid of at least two sensors, the basis weight cross-direction profile and the basis weight longitudinal direction profile of the paper web are measured, whereby a possible deformation of the headbox is inferred or determined from a relevant wavelength of the change in the basis weight cross-direction profile, and in order to verify this change in the basis weight cross-direction profile. The course of the basis weight longitudinal direction profile is determined at the location of this at least one maximum of the change in the basis weight cross-direction profile and the change speed and/or the change frequency at this location is determined from the characteristic chronological course of the basis weight, or the basis weight longitudinal direction profile, in order to infer or determine a possible deformation of the headbox and therefore an influence on the fiber orientation cross-direction profile.
Another feature of the invention is to provide a device for detecting a change in the fiber orientation cross-direction profile of a paper or cardboard web in the manufacturing process on a paper or cardboard manufacturing machine is attained by virtue of the fact that the device includes at least one sensor for measuring the basis weight cross direction profile of the web or a cross-direction profile of a correlated quantity. Furthermore, the device includes an arrangement for determining the change(s) in the cross-direction profile of the basis weight or a quantity that correlates to a change or changes in the cross-direction profile of the basis weight; at least one device for determining the wavelength xcex of the change(s) and in addition, an arrangement for comparing the wavelengths of the cross-direction profile of the changes to a predetermined value raster for deciding whether the respective change in the basis weight cross-direction profile can correspond to a change in the fiber orientation cross-direction profile and in addition, an output unit for indicating the change in the fiber orientation cross-direction profile.
According to another feature of the invention, the above-mentioned arrangements may include, for example, an arithmetic unit with corresponding computing programs, for example computing modules. Preferably, a Fourier analysis is carried out to determine the wavelengths and the spectral result of the Fourier analysis is evaluated in accordance with the above-described process.
In a simplified aspect of the invention, the device for detecting a change in the fiber orientation cross-direction profile of a paper or cardboard web in the manufacturing process has at least one sensor with an evaluation unit for determining the chronological course of the basis weight in the travel direction of the web in at least one position with regard to the machine width, has at least one unit for determining the change speed xcex94FG/xcex94T, or the relative change speed of the basis weight in this at least one position with regard to the machine width, and also has at least one device for comparing the change speed(s) to a predetermined value raster for deciding whether the respective change speed can correspond to a change in the fiber orientation cross-direction profile and has an output unit for indicating the change in the fiber orientation cross-direction profile.
Another aspect of the device according to the invention for detecting a change in the fiber orientation cross-direction profile of a paper or cardboard web in the manufacturing process, has at least one arrangement for determining the basis weight cross-direction profile of the web or a cross-direction profile of a quantity that correlates to the basis weight cross-direction profile of the web, at least one arrangement for determining the chronological course of the basis weight in the longitudinal direction of the web in at least one position with regard to the machine width, at least one arrangement for determining the change speed or the relative change speed of the basis weight in this at least one position with regard to the machine width, at least one unit for comparing the change speed(s) to a predetermined value raster, and also a unit for deciding whether the respective change speed of the basis weight can correspond to a change in the fiber orientation cross-direction profile and an output unit for indicating the change in the fiber orientation cross-direction profile.
Another feature of the device for detecting a change in the fiber orientation cross-direction profile of a paper or cardboard web in the manufacturing process has, according to the invention, at least two sensors and at least one evaluation unit for determining the basis weight cross-direction profile and the basis weight longitudinal direction profile of the paper web, at least one unit means for determining a relative wavelength that indicates a change in the basis weight cross-direction profile due to a possible deformation of the headbox, and also at least one unit for determining the course of the basis weight longitudinal direction profile at the position of the at least one maximum of the change in the basis weight cross-direction profile and for verifying that a possible deformation of the headbox and therefore an influence on the fiber orientation cross-direction profile can be inferred or determined from the characteristic chronological course of the basis weight or from the change speed of the basis weight; and also includes an output unit for indicating the change in the fiber orientation cross-direction profile.
Other features of the invention include providing a process for detecting a change in fiber orientation cross-direction profile of a paper or cardboard web in a manufacturing process on a paper or cardboard manufacturing machine. Aspects of this invention include determining a change in the fiber orientation cross-direction profile in the web by determining a change in at least one of a characteristic change in a basis weight cross-direction profile and a characteristic change in the basis weight in a travel direction of the web. At least one measured quantity correlated to the characteristic change n the basis weight cross-direction profile and the characteristic change in the basis weight in the travel direction of the web is interchangeable with the characteristic change in the basis weight cross-direction profile and the characteristic change in the basis weight in the travel direction of the web.
Included in the other features is a process involving repeatedly determining a basis weight cross-direction profile of the web, determining change in the basis weight cross-direction profile, determining wavelengths of the change in the basis weight cross-direction profile, and comparing the wavelengths of the change in the basis weight cross-direction profile to a predetermined value raster for determining if the change corresponds to a change in the fiber orientation. Another feature relates to determining that a change n the fiber orientation cross-direction profile has occurred when the wavelength of the change in the basis weight cross-direction profile is greater than a predetermined value and, determining that the fiber orientation cross-direction profile is unchanged when the wavelengths in the basis weight cross-direction profile is less than a predetermined value.
Also included in the features is determining a chronological course of a basis weight of the web in at least one position of the web with respect to a width of the machine, determining a chronological change in the basis weight in the at least one position, determining one of a change speed and a relative change speed of the basis weight in the at least one position and comparing one of the change speed and the relative change speed to a predetermined value raster for determining if one of the change speed and the relative change speed corresponds to a change in the fiber orientation cross-direction.
Another feature of the invention determines that a change in the fiber cross-direction profile has occurred when one of the change speed and relative change speed of the basis weight at one position is greater than a first predetermined value and less than a second predetermined value.
Another aspect involves repeatedly determining a basis weight cross-direction profile of the web, determining change in the basis weight cross-direction profile, determining wavelengths of the change in the basis weight cross-direction profile and comparing the wavelengths of the change in the basis weight cross-direction profile to a predetermined value raster for determining if the change corresponds to a change in the fiber orientation.
Another feature is determining that the change in the fiber orientation cross-direction profile has occurred when the wavelength of the change in the basis weight cross-direction profile is greater than a first predetermined value and less than a second predetermined value, and determining that the change in the giver cross-direction profile has occurred when one of the change speed and the relative change speed of the basis weight at one position is greater that a predetermined value and less than another predetermined value.
A further feature is measuring a basis weight cross-direction profile and a basis weight longitudinal direction profile of the paper web by using at least two sensors, determining existence of deformation of a headbox in a machine manufacturing the paper web by determining a wavelength of a change in the basis weight cross-direction profile, determining a course of the basis weight longitudinal direction profile at a position of a maximum change in the basis weight cross-direction profile and determining the existence of deformation of the headbox and influence of the deformation on the fiber orientation cross-direction profile from one of a characteristic chronological course of the basis weight and change of speed of the web.
Another aspect of the process determines a change in the basis weight indirectly by determining a change in a gap width profile of an orifice at an outlet gap of a headbox nozzle in the machine and determining a change in the basis weight indirectly by determining a change in a flow rate of solids in sections of a headbox in the machine.
Other features include counteracting the change in the fiber orientation cross-direction profile by adjusting an orifice in a headbox of the machine, counteracting the change in the fiber orientation cross-direction profile by changing a flow rate of a stock suspension in at least one section of a headbox in the machine, the flow rate of the stock suspension is either increased or decreased in at least one section of the headbox, and correcting a change in the basis weight cross-direction profile and the fiber orientation cross-direction profile in at least one position of the traveling paper web, by using a sectionally stock density-regulated headbox of the paper or cardboard web manufacturing machine, including an adjusting element for sectionally influencing an outlet gap of the headbox, and during correcting of the basis weight cross-direction profile, in order to detect a change in the fiber orientation cross-direction profile, the process for detecting a change in the fiber orientation cross-direction Is performed so that when a change in the fiber orientation cross-direction profile is positively detected, a correction of the basis weight cross-direction profile is performed by adjusting the outlet gap of the headbox, when a change in the fiber orientation cross-direction profile is unnecessary, the correction of the basis weight cross-direction profile is performed by changing a profile of the stock density.
Another feature of the invention is correcting a change in the basis wight cross-direction profile and the fiber orientation cross-direction profile in at least one position of the traveling paper web, with a sectional stock density-regulated and sectional volume flow-regulated headbox, and during correcting of the basis weight cross-direction profile, in order to correct a change in the fiber orientation cross-direction profile, the detection process is performed so that when a change in the fiber orientation cross-direction profile is detected, a correction of the basis weight cross-direction profile is performed by changing the sectional volume flow in the headbox, and when a change in the fiber orientation cross-direction profile is unnecessary, the correction of the basis weight cross-direction profile is performed by changing a profile of the stock density.
Yet another feature of the process is determining one of the basis weight cross-direction profile of the web and a cross-directional profile of a correlated measured quantity by using at least one sensor, determining the change in one of the cross-direction profile of the basis weight and the correlated measured quantity by using at least one determining unit, determining wavelengths of the changes by at least one wavelength measuring device, comparing the wavelengths of the cross-direction profile of the changes to a predetermined value raster for determining if the change corresponds to a change in the fiber orientation cross-direction profile by using a comparing unit and indicating the change in the fiber orientation cross-direction profile in an output unit.
Another feature of the invention is to provide an apparatus for detecting a change in a fiber orientation cross-direction profile in at least one position in a paper or cardboard web in the manufacturing process on a paper or cardboard manufacturing machine, the device including at least one sensor having an evaluation unit for determining a chronological course of a basis weight in a traveling direction of the web in at least one position with regard to a width of the machine, at least one determining unit for determining at least one of a change speed and a relative change speed of the basis weight in said at least one position with respect to the width of the machine, at least one comparing unit for comparing the change speed to a predetermined value raster for determining if the change speed can correspond to a change in the fiber orientation cross-direction profile, and an output device for indicating a change in the fiber orientation cross-direction profile.
Another feature is a device for detecting a change in a fiber orientation cross-direction profile of a paper or cardboard web in a manufacturing process on a paper or cardboard manufacturing machine including at least one determining unit for determining a chronological course of a basis weight in a longitudinal direction of the web in at least one position with respect to a width of the machine, at least one determining element for determining one of a change speed and a relative change speed of the basis weight in at least one position with respect to the width of the machine, at least one comparing unit for comparing the change speed to a predetermined value raster, a determining unit for determining if the change speed of the basis weight corresponds to a change in the fiber orientation cross-direction profile, and an output device for indicating the change in the fiber orientation cross-direction profile.
Another feature includes at least two sensors and at least one evaluation unit for determining a basis wight cross-direction profile and a basis wight longitudinal direction profile of the paper web, at least one wavelength determining unit for determining a wavelength indicative of a change in the basis weight cross-direction profile and a deformation of a headbox of the machine, at least one course determining unit for determining a course of the basis weight longitudinal direction profile at the position of a maximum change in the basis weight cross-direction profile and for verifying a deformation of the headbox and a change in the fiber orientation cross-direction profile being determined from a characteristic chronological course of one of the basis weight and the change speed of the basis weight and, an output unit for indicating the change in the fiber orientation cross-direction profile.
Yet other features of the device include an arithmetic unit including one of an evaluating program and an evaluation sub-program, a controlled motion unit for controlling motion of the at least two sensors in a direction lateral to a direction of the machine, and a first sensor is moveable lateral to a direction of the machine and another sensor is stationary with respect to the machine.
Other features include at least one of the sensors provided in a region of a stock suspension stream emanating from a headbox supplying a suspension to the machine, at least one of the sensors being provided in a region of a former portion and in a region of a press portion of the paper or cardboard web manufacturing machine. Also, at least one of the sensors is provided in a region between a former and a press section and at least one of the sensors is provided in a region between a press section and a drying section of the paper or cardboard web manufacturing machine, and at least one of the sensors measures at least one of stock density, absorption of radioactive radiation, light, ultrasound or for measuring the stream density and the stream speed.